Characteristics of Earth Potential Difference Generations by Seismic Wave

Abstract

To clarify the relationship between earthquakes and electric phenomena the earth potential difference (EPD) has been observed continuously at Aobayama in Sendai and Tsukidate, 60km north of Sendai. A new measuring method of the EPD is used to reduce the unnecessary signals induced by artificial and natural earth current sources. We have noticed just the EPD variational signals induced by seismic waves. On all earthquakes of more than 1 of JMA (Japan Meteorological Agency) intensity scale we can clearly observe EPD signals. The P-wave arraival times agree quite well with ones obtained by the seismograph at Meteorological Agency Seismograph. The EPD signals of Kobe earthquake, though less than 1 scale, have been clearly recorded at the both observatories points. The EPD signals are also observed at three different positions under the ground. We have found interesting electric field characteristics caused by seismic waves as follows; (1) the electrical field in the vertical direction is higher than in the horizontal direction by one order (2) this field increases rapidly coming up to the ground surface.